Pressure-sensitive adhesive constructions made without a separate release liner are comprised of a two sided substrate with an adhesive on one side and a release material on the other. These are commonly referred to as self-wound products in the industry. The substrate can be made from paper, plastic, metal, cloth, combinations of these materials and other materials. The pressure-sensitive adhesive layer is inherently tacky at room temperature and can bond with other surfaces with light hand pressure. Both permanent and removable adhesives can be used depending on the intended application for the product. For removable adhesives primers can additionally be used to increase the anchorage between the adhesive and the two sided substrate. Release agents are usually applied to the opposite side of the substrate to enable ready unwinding of the self-wound construction. Some low surface energy substrates are inherently releasable but most require the use of a release agent. If the release agent is not used, the adhesive will bond to the backside of the substrate and prevent the roll from unwinding. The force required to unwind the roll is dependent on the specific surface characteristics and chemical compatibility of the adhesive with the release agent.
The postage stamp is a rather complex device. To meet current user demands it must be constructed of a face material or backing capable of accepting high quality printing of complex design. The stamp must also be stable under a variety of environmental conditions and provide an ink-cancelable surface on which the cancellation ink dries rapidly. It is also desired that the stamp can be separated from its adhesive to meet the needs of stamp collectors. In addition to being cancelable, the stamp should have means to detect the stamp so that a properly stamped envelope can be cancelled in an automated cancellation machine. The means to detect the stamp may be either in the ink cancelable surface or in the paper used to prepare the stamp prior to printing.
Traditionally, postage stamps have been manufactured with a water-soluble, water-activated adhesive. It has been the desire of the postal service to not only convert the adhesive to a self-adhesive or pressure-sensitive adhesive, but to also present such postage stamps in traditional and new formats. One new format provides self-adhesive stamps which are dispensable from an automatic teller machine. An old format provides stamps which are dispensable from a self-wound tape or roll.
A self-wound construction comprises a tape which, in the case of stamps, provides a plurality of contiguous stamps marked at regular intervals along the length thereof to indicate where a die-cut is to be made to separate the stamps or with a perforation die-cut between each stamp. The back surface of the stamps is coated with a layer of pressure-sensitive adhesive. The opposed or face surfaces of the stamps must provide an ink-cancelable surface. When the stamps are wound on themselves to form a roll, the pressure-sensitive adhesive comes into contact with the face surface of another stamp. The adhesive adheres to the face, and it is then difficult to impossible to unwind the roll without damage to the face or printed surface. It is possible to reduce the adhesion of the pressure-sensitive adhesive to the face surface of the stamp constructions by applying a release coating to the face surface of the stamps which is capable of reducing the strength of adhesive bond between the pressure-sensitive adhesive and the face of the stamp construction when in the form of a self-wound tape or roll.
U.S. Pat. No. 5,165,976 describes a substrate which is provided with a release surface by application of an emulsion of a vinyl-addition silicone system, catalyst therefore, and a particulate component which may be inorganic or organic in nature but which is preferably a resin. The vinyl-addition silicone system is cured by application of heat and removal of water. The products are useful for many release applications, especially pressure-sensitive adhesive roll stock, and can be converted at high speeds.
U.S. Pat. No. 5,356,706 describes a modified silicone copolymer useful as a release agent. The modified silicone is the reaction product of a di-omegaorgano functional dimethylsiloxane oligomer having terminal active hydrogen groups, a carboxyl group bearing monomer, and a diisocyanate. The copolymer is reported to provide good release properties from tacky adhesive masses.
The present invention is directed to providing ink-imprintable release coating compositions and an ink-cancelable release surface for application to the face side of pressure-sensitive adhesive stamp constructions.